The increasing demand for energy, limited fossil fuel supplies, environmental pollution and global climate change leads to a growing interest in renewable resources, including wood biomass utilization for production of energy and biomaterials as well as for replacement of existed hazardous materials for environmental protection.  One of the representatives of wood biomass is technical lignins obtained as wood by-products during cellulose pulping. According to the analysis of the patenting activity of the last years, utilization of lignins for obtaining surface active agents (SAAs) (dispersants, emulsifiers, detergents and foaming agents) takes the first place in comparison with their usage in resins, composites, concrete as well as for obtaining chemicals,  etc. Due to the features of a lignin chemical structure and low molecular masses, lignins effectively replace hazardous synthetic SAAs negatively affecting on the environment and polluting the aquatic flora and fauna.

In the present work, the effect of hydrolysis of hardwood sawdust on surface active properties of soda lignin at the gas-liquid and liquid-liquid interfaces within a wide pH and ionic strength range has been investigated. The pre-hydrolysis of wood was done to enhance the yield of hemicelluloses with the aim of the wood biorefinery. It was found that the surface activity of soda lignin at the gas-liquid interface grown with decreasing the рН values and increasing the ionic strength. Simultaneously, the average sizes of the lignin particles in the aqueous solutions increased, but the values of their zeta potential decreased, due to lowering the ionization degree of the lignin’s acidic groups and self-assembling the lignin nanoparticles. The growth of hydrophobicity of the soda lignin enhanced the surface pressure at the air-water interface and led the formation of a rigid polymeric film at the interface in acid media. The behaviour of the soda lignin at the liquid-liquid interface for stabilisation of the “rapeseed oil-in-water” emulsion had shown its dependence on the lignin concentration and pH values of its solution. With decreasing the concentration and increasing the pH of the lignin solutions from the neutral to alkaline medium, a zeta  potential values of the O/W emulsions samples  achieved more than - 90 mv that indicated their enhanced colloidal stability. The obtained results testified the prevailed electrostatic mechanism of the O/W emulsion stabilization with the diluted alkaline solutions of the soda lignin.

DOI: https://doi.org/10.3846/enviro.2017.033